All-optical free-space cross-connect switches typically consist of a fabric of optical emitters that launch a collimated beam, and another fabric of optical receivers. The emitters can be selectively connected to the receivers by varying the direction of the collimated beam so as to impinge on the selected receiver. Any combination of active and/or passive emitters and/or receivers can be combined to form 1×N, N×1, or N×N switch assemblies.
All-optical free-space cross-connect switches have been reported that either redirect a collimated beam that is launched in a fixed direction, or control the direction of a collimated beam. Switches that redirect a collimated beam typically rely on an arrangement of micro-mirrors that can be tilted, typically by applying an electrostatic force. Conversely, switches that control the beam direction have optical emitters that rotate or tilt in response to an applied actuation signal or change, the position of an optical emitter, such as a fiber tip, relative to the optical axis of a collimating lens, which varies the angle of the beam. Both types of optical switches can advantageously employ Micro-Electro-Mechanical Systems (MEMS) technology, with actuation provided by mechanical, electromagnetic, piezoelectric, photoactive ceramic or polymer, thermal, chemically-active polymer, electrostrictive, shape-memory alloy or ceramic, hydraulic and/or magneto-restrictive actuators and other types of actuators known in the art.
Micro-mirror devices are typically etched from a Si wafer, with the mirror elements formed as hinged reflection-coated platelets which have a poorly defined rest position and tend to flex when actuated, causing the redirected beam to loose collimation. The mirror devices are also essentially undamped which limits their response time.
Recently, optical emitters with a controlled beam pointing direction have been proposed that incorporate piezoelectric actuators. Piezoelectric actuators advantageously provide a fast response, produce large forces, have a high characteristic frequency for fast switching, and have a well-defined rest position. Additionally, they are low-cost and have low susceptibility to vibration. Movement of the piezoelectric actuator can be controlled by applying electrical charges to electrodes. For example, U.S. Pat. No. 4,512,036 describes bending the free end of a fiber in two directions perpendicular to the longitudinal axis of the fiber, with the fiber tip moving relative to a stationary lens. Other devices propose using piezoelectric actuators to move a lens in front of a stationary fiber in a plane perpendicular to the longitudinal axis of the fiber. However, practical piezoelectric actuators tend to have a limited displacement range, which limits the attainable tilt angle of the optical beam and hence also reduces the switching speed of the cross-connect switch and increases the sensitivity to vibration.
It has been proposed to amplify the displacement or stroke produced by piezoelectric actuators to increase the beam tilt angle. For example, U.S. Pat. No. 4,303,302 describes a simple lever arm with an optical fiber attached to the arm which is supported on its fixed end and mechanically coupled to a piezoelectric bimorph bending element near the fixed end of the lever arm. The free end of the lever arm with the end of the optical fiber could thereby move in a plane and be aligned with different optical fibers located on an arc. A different lever mechanism for increasing the tilt angle of a Gimbals-mounted fiber holder with a fiber/lens assembly emitting a collimated optical beam is proposed in PCT/GB01/00062. Such lever mechanisms, however, increase the mass to be moved by the piezoelectric transducer and hence disadvantageously reduce the characteristic frequency of the optical assembly and therefore also the switching speed of the cross-connect switch.
The aforedescribed piezoelectric actuation mechanisms with levers are unlikely to benefit from inexpensive and reproducible batch fabrication processes, such as MEMS technology. With MEMS, mechanical elements, sensors, actuators, and electronics can be integrated on a common substrate using the micromachining technology derived from IC fabrication processes. Reliable high-performance products can be designed and optimized using computer automatic design tools, such as AutoCAD and the like.
The size of MEMS devices can range from several micrometers to millimeters, and can be precisely controlled by lithographic and etching processes that are standard in the semiconductor industry. Such miniaturization is particularly attractive for accurate actuation as well as optical sensing and positioning. In particular, miniaturization reduces size and increases port density of an all-optical switch, and can be extended to other tunable and/or programmable optical components in optical networks.
It would therefore be desirable to provide a piezoelectrically actuated motion transformer for beam steering and positioning in all-optical cross-connect switches that has a sufficient large beam deflection angle for a high port count and a fast switching speed and that can be manufactured reproducibly and inexpensively by conventional MEMS fabrication processes.